| Posted | Nick | Remark | |
|---|---|---|---|
| #openstack-nova - 2017-09-27 | |||
| 13:22:34 | efried | johnthetubaguy But in fact, one VCPU is being consumed by a VM that was spawned out of band | |
| 13:22:36 | rgerganov | mriedem, that may work for vcpu and memory but it won't work well for storage | |
| 13:22:45 | johnthetubaguy | its the out of band VMs, I thought we explicitly didn't support that | |
| 13:23:03 | efried | johnthetubaguy Yeah, bauzas said the same, but didn't find where that's documented. | |
| 13:23:11 | efried | Not saying that means it's supported, or that it should be :) | |
| 13:23:40 | bauzas | so, Nova isn't a proxy layer for hypervisors | |
| 13:23:49 | johnthetubaguy | yeah, I could have swarn it was in here, but I don't see it: https://docs.openstack.org/nova/latest/contributor/project-scope.html | |
| 13:24:08 | bauzas | johnthetubaguy: yeah, I verified that | |
| 13:24:14 | bauzas | lemme provide a change for it | |
| 13:24:25 | johnthetubaguy | well, its a bit late I guess | |
| 13:25:13 | cdent | So, even if the statement is “we don’t do that” the problem still holds for shared storage | |
| 13:25:21 | efried | right | |
| 13:25:22 | mriedem | nova doesn't import existing vms on the hypervisor, | |
| 13:25:37 | mriedem | but that doesn't mean we don't try to adjust inventory based on things running on the hypervisor host | |
| 13:25:37 | cdent | where “the problem” is the generic notion of mixed accounting | |
| 13:25:39 | efried | mriedem Which actually makes it more problematic. | |
| 13:25:40 | efried | right. | |
| 13:25:43 | johnthetubaguy | cdent: yeah, that sounds like a real thing we have to support | |
| 13:25:43 | mriedem | that's why we have reserved | |
| 13:25:48 | efried | right | |
| 13:26:08 | mriedem | even libvirt hosts have to account for things like ovs running on the same host | |
| 13:26:09 | cdent | Right, so one of the underlying questions is: | |
| 13:26:21 | cdent | Do we intend/expect that reserved will by dynamically adjuted, frequently | |
| 13:26:43 | cdent | Or in the cases where we want it to be dynamically adjusted we should instead make allocations, via some third party? | |
| 13:26:45 | efried | Right, back to what johnthetubaguy mentioned earlier: "not doing live updates of resource usage" | |
| 13:27:06 | efried | That is, will get_inventory() eventually be a thing that's run only once, rather than on a periodic? | |
| 13:27:15 | cdent | exactly | |
| 13:27:17 | bhagyashris | johnthetubaguy, mriedem: Could you please review patch: https://review.openstack.org/#/c/409644/ ? Addressed all review comments. Thank you :) | |
| 13:27:23 | mriedem | i don't think it will no | |
| 13:27:27 | bauzas | I'm not seeing the reserved bit to be that dynamicv | |
| 13:27:31 | mriedem | the operator can adjust reserved space dynamically | |
| 13:27:35 | johnthetubaguy | cdent: I separate allocations are easier to update than a single reserved value | |
| 13:27:42 | efried | I've heard tell (possibly from jay) that it's a no-no to update the *total* amounts. | |
| 13:27:44 | mriedem | we talked about this in boston | |
| 13:27:56 | bauzas | but yeah, the operator can just set or raise the reserved bit when they want | |
| 13:27:58 | mriedem | about how we don't account for overhead, and operators would have to handle that by toggling reserved values | |
| 13:28:23 | cdent | mriedem: yes, but the new ingredient here is the dynamism | |
| 13:28:25 | cdent | maybe | |
| 13:28:27 | bauzas | mriedem: do you think we should clearly state that in https://docs.openstack.org/nova/latest/contributor/project-scope.html ? | |
| 13:28:40 | efried | ...unless, like, they hot-plug a whole new disk, or jack up the disk size on the SAN or whatever. In that case, we should be able to bump the totals, yes? | |
| 13:28:43 | bauzas | the fact that Nova doesn't support direct hypervisor VMs, but can leave room for them | |
| 13:28:49 | cdent | efried: yes | |
| 13:28:56 | efried | Same actually applies to CPUs | |
| 13:29:30 | efried | Not sure if more primitive hypervisors have this, but there's a dynamic entitlement thing where you can unlock previously-unavailable CPUs on the fly. | |
| 13:29:35 | johnthetubaguy | bhagyashris: there was a -1 review on that patch with no answer when I last looked, so I skipped looking any deeper, did you respond to their questions yet? | |
| 13:30:28 | johnthetubaguy | mriedem: it totally feels like the toggling reserved values ticks the 80% case, with very few surpizes | |
| 13:31:02 | cdent | efried, mriedem, bauzas, johnthetubaguy, rgerganov: it feels like we probably have the tooling to make something workable for this, but as we figure it out it would be good to document some kind of (hate this phrase) best practice, | |
| 13:31:32 | efried | Me, I'm concerned about the penalty of getting the full list of instances every time get_inventory is run. | |
| 13:32:35 | johnthetubaguy | its feels like making the 80% case work really well should be step 1? And some rough best practices for the other bits for now, that could work. | |
| 13:33:01 | cdent | efried: instances from the hypervisor’s point of view, nova’s point of view or placement’s point of view? or some combination? That is, which one worries you most? | |
| 13:33:18 | johnthetubaguy | honestly doing both of those worry me | |
| 13:33:46 | efried | Yeah, I have to do both. | |
| 13:33:47 | johnthetubaguy | I like the system doing nothing when its idle, in an ideal world of course. | |
| 13:33:58 | bauzas | we shouldn't really create a way where people would directly call their VMs if they wish, because that would mean we would silently say we support that | |
| 13:34:20 | efried | Cause the alternative is maintaining some kind of cache and trying to keep it up to date every time a VM gets spawned or deleted (I can get notifications for the OOB ones, and update the in-band ones from spawn/destroy). | |
| 13:34:38 | bhagyashris | johnthetubaguy: Actually I have not respond yet, but Andrey Volkov is given -1 and he suggested that we can fix this issue at schema level (same thing I have proposed in the patch set 3) but after some discussion we decided to fix this in logic and at schema level. | |
| 13:34:44 | bauzas | if the operator doesn't know the dedicated amount their wanna reserve, then either they should disable some compute from the pool, or just set a high value | |
| 13:35:18 | johnthetubaguy | but isn't the easy case much easier here? deployer sets the reserved values, no period updates, worry about special cases later? | |
| 13:35:19 | bauzas | providing a way to dynamically adjust resources in Nova would just mean we create things to support | |
| 13:35:23 | cdent | johnthetubaguy, bauzas: perhaps sad, but true, there are in tree hypervisors where oob vms are fairly common. nova in itself may not need to support that, but the hypervisors will likely continue doing it | |
| 13:35:25 | bhagyashris | s/and at schema level/and not at schema level | |
| 13:35:50 | bauzas | johnthetubaguy: that's my point | |
| 13:36:08 | dansmith | mriedem: have you seen the stuff I added to the etherpad last night? | |
| 13:36:22 | bauzas | johnthetubaguy: if operators really want a space for out-of-band VMs, then they have the reserved bit they can set and try to modify when they feel necessary | |
| 13:36:43 | bhagyashris | johnthetubaguy: i will respond to that question. | |
| 13:36:54 | johnthetubaguy | cdent: but even those drivers, there are folks who run dedicated clusters just for OpenStack | |
| 13:36:54 | bauzas | but trying to provide some mechanism for having a dynamic reserved bit seems to me something we shouldn't do | |
| 13:37:41 | bauzas | and honestly, wouldn't it be better to just disable a host and play with it, if that's really needed ? | |
| 13:37:44 | cdent | johnthetubaguy: yes, totally | |
| 13:37:47 | johnthetubaguy | cdent: that was me arguing for making the sync optional, for when you know Nova owns the world | |
| 13:37:58 | rgerganov | johnthetubaguy, most users runs dedicated clusters but also used shared storage | |
| 13:38:07 | dansmith | johnthetubaguy: are you talking about the periodic that will try to delete unknown vms? | |
| 13:38:09 | mriedem | dansmith: sure did | |
| 13:38:14 | johnthetubaguy | bhagyashris: thanks, responding in the review will help wehn I get back to that | |
| 13:38:21 | mriedem | dansmith: nope, talking about update_available_resource | |
| 13:38:41 | mriedem | and using get_inventory to report reserved space for other things running on the hypervisor outside of nova's control | |
| 13:38:41 | johnthetubaguy | dansmith: well, I was thinking about that early, with all the logging by default, but there I was meaning the resource tracker updater | |
| 13:39:10 | dansmith | mriedem: eff that. there's a reserved count for that kind of stuff. | |
| 13:39:17 | bhagyashris | johnthetubaguy: Thank you :) | |
| 13:39:34 | mriedem | dansmith: meaning the config option? | |
| 13:39:48 | dansmith | meaning counting other things and subtracting it ourselves | |
| 13:40:02 | mriedem | i think the config option is what's used to report reserved inventory in the RT today | |
| 13:40:13 | dansmith | yes | |
| 13:40:33 | dansmith | well, actually, I dunno that it is today, but it should be, and that should be your outlet to carve out space | |
| 13:41:12 | dansmith | it is | |
| 13:41:17 | dansmith | https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L102-L125 | |
| 13:41:39 | dansmith | make those hot-reloadable if you want, but that's the path, IMHO | |
| 13:42:58 | efried | dansmith That guy still gets run on a periodic basis, right? I.e. dynamic tweaking of reserved amounts is supported (at least by the driver - not asking if those conf opts are dynamic) | |
| 13:43:31 | johnthetubaguy | we should make SIG_HUP trigger a resource refresh? | |
| 13:43:46 | dansmith | johnthetubaguy: HUP already triggers a config re-read | |
| 13:43:54 | johnthetubaguy | I was meaning a resource tracker update | |
| 13:44:03 | dansmith | johnthetubaguy: so if they were reloadable you'd get a new value the next time inventory runs | |
| 13:44:07 | johnthetubaguy | so we don't have to keep the periodic thing, just do it on events | |
| 13:44:30 | dansmith | I'm not sure there's any reason not to do it perioically | |
| 13:44:53 | johnthetubaguy | system load, all that lists of instances, etc | |
| 13:45:28 | dansmith | it doesn't need to anymore | |
| 13:46:00 | dansmith | in pike, once there aren't any ocata computes around we're not doing healing for instances other than deleted ones | |
| 13:46:31 | johnthetubaguy | I guess I am confused | |
| 13:47:24 | johnthetubaguy | I thought we were left with no periodic updates in queens | |
| 13:47:31 | johnthetubaguy | to inventory, etc | |